This invention relates to an image forming machine such as laser printer, facsimile, or electrostatic copier. More specifically, the invention relates to an image forming machine which can form images on both surfaces of a sheet, and by which the sheet having an image or images formed on one or both of its surfaces can be discharged after posttreatment of the sheet, such as punching, stapling, or sorting.
In an image forming machine, such as an electrostatic copier (hereinafter referred to as a copier), there may be need to not only discharge a sheet having an image formed thereon (a copied sheet) onto a copy receiving tray, but also perform sheet posttreatment, such as punching, stapling, or sorting. In this case, a finisher (a sheet post-treating device) is produced independently of the copier, and is provided detachably on a lateral side part of the copier.
In a copier, the height of a sheet discharge port differs generally depending on the entire size of the copier. When the copier is equipped with a finisher, it has been common practice to produce a specific finisher, which has a sheet send-in port with a height corresponding to the sheet discharge port of a copier of a specific size (type), and provide the copier of the specific size with the specific finisher.
There has been known a finisher, which is to be provided on a copier, and which has a punching means installed at an upstream position of a sheet send-in path, the punching means designed for punching as sheet posttreatment. With this type of finisher, a sheet having an image formed thereon is once stopped when it passes through the punching means. At the time of its stoppage, punching is performed for an end portion of the sheet. More concretely, the punching means has a sheet stopper. The sheet stopper is disposed so as to be selectively brought by a drive means, such as cam, to a retreat position at which the sheet stopper retreats from a sheet send-in path, and permits transport of the sheet sent in, and a stop position at which the sheet stopper protrudes into the sheet send-in path to block the sheet send-in path, and contacts one end of the sheet sent in, i.e., its downstream end in a transport direction of the sheet, to stop the movement of the sheet temporarily, thereby putting the sheet to a predetermined punched position. When the sheet stopper is located at the stop position with a predetermined timing with respect to the sending-in of the sheet, the sheet sent in is stopped at the punched position. Then, a punch of the punching means is reciprocated in a face-and-back direction of the sheet to carry out punching at a predetermined position of an end portion of the sheet, the downstream end portion of the sheet. The sheet punched at its one end portion is sent in, in a state turned upside down, onto a sheet receiving stand provided at the finisher. A pile of the punched sheets thus stored on the sheet receiving stand is discharged onto a discharge tray for sorting.
The above-described finisher having the punching means may be provided in a copier capable of forming images on both surfaces of a sheet. An example of this type of copier has an image forming transport path in which an image is formed on one surface of the sheet being transported, a reversing transport path in which a transport direction of the sheet selectively introduced from a downstream portion of the image forming transport path is reversed, a returning path in which the sheet reversely transported from the reversing transport path is returned below the image forming transport path with the directions of the face and back of the sheet being unchanged, and an inverting transport path in which the sheet returned through the returning path is turned upside down and readmitted into an upstream portion of the image forming transport path. The downstream end of the image forming transport path is connected to the sheet send-in path of the finisher provided on the copier. When the sheet having images formed on both surfaces thereof in the copier is to be punched, the sheet is sent in from the downstream end of the image forming transport path to the sheet send-in path of the finisher, and has its end portion is punched in the aforementioned manner.
As described above, the finisher provided on the copier is produced to be adapted for a specific copier. When it is installed actually, adjustment of its height is an essential task. Particularly in an unfavorable environment for installation, such as a place of installation with a slope or irregularities, this height adjusting work involves considerable labor and burden, thus taking a long time for installation. If, after installation of the finisher, a deviation in height occurs between the finisher and the copier, or a deviation arises in the gap between them, because of unexpected factors, transport of the sheet from the copier to the finisher may fail to be performed stably. In case the sheet is not stably transported, a jam may take place, or a defective product may occur. Since the finisher is installed at a side portion of the copier, moreover, a lateral surplus space for installation is needed. Furthermore, in dealing with the jam, it is necessary to separate the finisher from the copier laterally. Thus, the above lateral space will have to be expanded further.
In a copier capable of image formation on both surfaces of a sheet and provided with a finisher having punching means, when punching is to be performed in an end portion of a sheet having an image formed only on one surface thereof during its transport through an image forming transport path of the copier, the sheet is fed into the finisher from a downstream end of the image forming transport path. The end portion of the sheet sent into the finisher is brought into contact with the sheet stopper of the punching means located at the stop position, and stopped at the punched position. Then, punching is carried out at a predetermined position of the end portion of the sheet. When punching is to be performed in an end, portion of a sheet having images formed on both surfaces thereof, the sheet having an image formed on one surface thereof during its transport through the image forming transport path of the copier passes through the reversing transport path and the returning path. Then, the sheet is turned upside down in the inverting transport path, and readmitted into an upstream portion of the image forming transport path. During its re-transport through the image forming transport path, an image is formed on the other surface of the sheet. The sheet having images formed on both surfaces thereof is sent into the finisher from a downstream end of the image forming transport path, and punching is performed at a predetermined position of an end portion of the sheet by the punching means in the manner stated earlier.
As clear from the foregoing description, the distance of transport during which the sheet has images formed on both surfaces thereof in the copier, then enters the finisher, and contacts the sheet stopper of the punching means is about twice or more as long as the distance of transport during which the sheet has an image formed on only one surface thereof, then enters the finisher, and contacts the sheet stopper of the punching means. Furthermore, transport of the sheet in double-sided image formation involves the inverting action of the sheet. As the sheet transport distance increases, there is a high possibility that displacement of the sheet in a horizontal direction perpendicular to the direction of transport (hereinafter referred to as xe2x80x9ctransport width directionxe2x80x9d) will increase during transport of the sheet. If the inverting action is involved during transport of the sheet, this possibility will be increased further. Consequently, the sheet having images formed on both surfaces thereof is transported over such a long distance of transport with its inverting motion being involved, and is brought into contact with the sheet stopper of the punching means in the finisher, whereby the sheet is stopped at the predetermined punched position. In this state, the possibility increases that displacement of the sheet in the transport width direction will become greater than in the sheet having an image formed on one surface thereof. This makes it difficult to bring the sheet to the predetermined punched position accurately, thus increasing variations, in the transport width direction, in the punch positions of a plurality of sheets that have been punched. As a result, a set of the punched plural sheets having images formed on both surfaces thereof and piled one on another suffer from a trouble, called hole misalignment, in which the punched holes of the sheets fail to align with a desired high accuracy. Thus, stable accuracy and quality of punching may fail to be ensured.
An object of the present invention is to provide a novel image forming machine which can perform posttreatment of a sheet without the need to produce a finisher independently and install it thereon, and thus does not require conventional finisher installation work, including a height adjustment task, and further achieves a space saving.
Another object of the invention is to provide a novel image forming machine which can transport a sheet stably while ensuring a sheet post-treating function, thereby reliably preventing a jam or the occurrence of a defective product.
Still another object of the invention is to provide a novel image forming machine which can use a sheet returning path concurrently as a send-in path to a sheet receiving stand to omit an independent send-in path to the sheet receiving stand, thus simplifying the structure of the machine and reducing costs.
A further object of the invention is to provide a novel image forming machine which can punch a plurality of types of sheets having images formed on both surfaces thereof, and pile the sheets to make a set of sheets having holes aligned with a desired high accuracy, thereby reliably preventing hole misalignment, so that stable accuracy and quality of punching can be ensured.
According to an aspect of the invention, there is provided an image forming machine having an image forming transport path in which an image is formed on one surface of a sheet being transported, a reversing transport path in which a transport direction of the sheet selectively introduced from a downstream portion of the image forming transport path is reversed, a returning path in which the sheet reversely transported from the reversing transport path is returned below the image forming transport path with the directions of the face and back of the sheet being unchanged, and an inverting transport path in which the sheet returned through the returning path is turned upside down and readmitted into an upstream portion of the image forming transport path, wherein:
a finisher including a sheet receiving stand placed below the returning path is provided, and at least one send-in means for selectively sending in the sheet, returned through the returning path, onto the sheet receiving stand is disposed in the returning path.
Preferably, a discharge path for discharging the sheet, which has been transported through the image forming transport path, onto a non-sorting discharge tray is disposed at a downstream end of the image forming transport path, a four-forked passageway is disposed at a downstream position of the image forming transport path, and a guide means is disposed on the four-forked passageway, the guide means being capable of selectively guiding the sheet, which has been transported through the image forming transport path, toward the discharge path, or the reversing transport path, or the returning path, and also selectively guiding the sheet, which has been introduced into the reversing transport path, toward the returning path.
Preferably, a plurality of return roller pairs are disposed in the returning path with spacing in a direction of returning, and the send-in means is composed of one of the return roller pairs, and a movable guide means which is disposed downstream from the one of the return roller pairs and which is selectively brought to a first guide position at which the movable guide means guides the sheet, returned by the one of the return roller pairs, toward the inverting transport path along the returning path, and a second guide position at which the movable guide means guides the sheet, returned by the one of the return roller pairs, toward the sheet receiving stand.
Preferably, a sorting discharge tray is disposed in a direction of extension of the sheet receiving stand, and the finisher has a catching means capable of catching an end of the sheet selectively sent in onto the sheet receiving stand by the send-in means and storing the sheet, and a sheet moving means capable of moving the sheet caught by the catching means toward the sorting discharge tray.
Preferably, the send-in means are disposed in the returning path at a plurality of positions corresponding to a plurality of types of sheets with different lengths in the direction of transport so that the plurality of types of sheets with different lengths in the direction of transport may be selectively returned, and the sheets may be selectively sent in toward the sheet receiving stand from the plurality of positions.
Preferably, a sheet post-treating means is placed in the other end portion of the sheet receiving stand, and a catching position of the catching means is put to a posttreatment position at which posttreatment by the sheet post-treating means is performed.
Preferably, the send-in means is disposed in the returning path at one position in one end portion of the sheet receiving stand facing the sorting discharge tray so that a plurality of types of sheets with different lengths in the direction of transport may be selectively returned, and the plurality of types of sheets with different lengths in the direction of transport may be selectively sent in from the one position, and the catching means is selectively moved to a plurality of catching positions, relative to the send-in means, corresponding to the plurality of types of sheets with different lengths in the direction of transport.
Preferably, a sheet post-treating means is placed in the other end portion of the sheet receiving stand, a catching position of the catching means corresponding to a sheet having a maximum length in the direction of transport is put to a posttreatment position at which posttreatment by the sheet post-treating means is performed, a catching position of the catching means corresponding to a sheet having a shorter length in the direction of transport than the maximum length in the direction of transport is set to be a predetermined catching position on the sheet receiving stand spaced by a predetermined distance from the posttreatment position toward the sorting discharge tray, and the sheets stored at the predetermined catching position by the catching means are moved to the posttreatment position by the sheet moving means to undergo posttreatment by the sheet posttreating means.
Preferably, a punching means is disposed at a downstream position in the image forming transport path.
According to another aspect of the invention, there is provided an image forming machine having an image forming transport path in which an image is formed on one surface of a sheet being transported, a reversing transport path in which a transport direction of the sheet selectively introduced from a downstream portion of the image forming transport path is reversed, and an inverting transport path in which the sheet transported through the reversing transport path is turned upside down and readmitted into an upstream portion of the image forming transport path, wherein:
a punching means is disposed at a downstream position in the image forming transport path.